1. Field of the Invention
This invention relates to the field of fasteners. More specifically, the invention comprises a fastener and companion component which cooperate to form a unidirectional latch.
2. Description of the Related Art
Mechanical fasteners are commonly used to pull two separate components together and hold them in a desired position. In such fasteners, threads are most commonly used to convert rotary motion into linear motion. However, simple camming surfaces may also be used for a “quarter-turn” type fastener. The present invention may be applied to many different types of prior art fasteners, including both threaded and camming types. However, for purposes of brevity, the following disclosure uses threaded fasteners to illustrate the preferred embodiments of the invention.
Threaded fasteners are designed to tighten when turned in a first direction and loosen when turned in the opposite direction. The most common thread pattern is a “right-hand thread,” in which the fastener is rotated in a clockwise direction to tighten. Those skilled in the art will know that fasteners which convert rotary motion to linear motion may not always remain in the tightened position. The shaft of such a fastener is placed in tension when the fastener is tightened. This tension may cause the fastener to rotate in the opposite direction over time—particularly when vibration or other cyclic motion is present. Thus, a prior art fastener may “back out” over time.
Concern over a fastener gradually working its way loose is particularly acute in the medical field, where threaded fasteners are often used to secure orthopedic hardware. It is known to secure such fasteners by tightening surgical wire over the head of the fastener and threading it through an existing or created orifice in adjacent bone. This is a time-consuming process which produces unpredictable results.
It is desirable to provide a fastener having an integral anti-rotation mechanism so that the fastener may be retained in a tightened state. It is also desirable to provide a means for defeating the anti-rotation mechanism when the user actually desires to remove the fastener. Finally, it is desirable to provide a relatively inexpensive anti-rotation mechanism so that the design may be employed in fields where low cost is a necessity. The present invention provides these features.